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Kinetics and Mechanism of the Anilinolysis of 1,2-Phenylene Phosphorochloridate in Acetonitrile
하시라니바라이,이해황 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.9
The nucleophilic substitution reactions of 1,2-phenylene phosphorochloridate (1) with substituted anilines (XC_6H_4NH_2) and deuterated anilines (XC_6H_4ND_2) are investigated kinetically in acetonitrile at –15.0 oC. The studied substrate of 1,2-phenylene phosphorochloridate is cyclic five-membered ring of phosphorus ester, and the anilinolysis rate of 1 is much faster than its acyclic analogue (4: ethyl phenyl chlorophosphate) because of extremely small magnitude of the entropy of activation of 1 compared to 4. The Hammett and Brönsted plots exhibit biphasic concave upwards for substituent X variations in the nucleophiles with a break point at X = 3-Me. The values of deuterium kinetic isotope effects (DKIEs; kH/kD) change from secondary inverse (kH/kD < 1)with the strongly basic anilines to primary normal (kH/kD > 1) with the weakly basic anilines. The secondary inverse with the strongly basic anilines and primary normal DKIEs with the weakly basic anilines are rationalized by the transition state (TS) variation from a predominant backside attack to a predominant frontside attack, in which the reaction mechanism is a concerted SN2 pathway. The primary normal DKIEs are substantiated by a hydrogen bonded, four-center-type TS.
하시라니바라이,이해황 대한화학회 2014 Bulletin of the Korean Chemical Society Vol.35 No.4
The kinetic studies on the reactions of O-methyl N,N-diisopropylamino phosphonochloridothioate with Xanilines and X-pyridines have been carried out in acetonitrile. The free energy relationship with X in the anilines exhibits biphasic concave upwards with a break region between X = (H and 4-F), giving unusual negative βX and positive ρX values with weakly basic anilines. The unusual phenomenon is rationalized by isokinetic relationship. A stepwise mechanism with a rate-limiting leaving group departure from the intermediate is proposed based on the selectivity parameter and variation trend of the deuterium kinetic isotope effects with X. The free energy relationship with X in the pyridines exhibits biphasic concave upwards with a break point at X = 3-MeO. A concerted mechanism is proposed based on relatively small βX value, and frontside and backside nucleophilic attack are proposed with strongly and weakly basic pyridines, respectively.
Kinetics and Mechanism of the Pyridinolysis of 1,2-Phenylene Phosphorochloridate in Acetonitrile
하시라니바라이,이해황 대한화학회 2012 Bulletin of the Korean Chemical Society Vol.33 No.1
The nucleophilic substitution reactions of 1,2-phenylene phosphorochloridate (1c) with X-pyridines are investigated kinetically in acetonitrile at –25.0 oC. The free energy correlations for substituent X variations in the nucleophiles exhibit biphasic concave upwards with a break point at X = 3-Ph. The pyridinolysis rate of 1c with a cyclic five-membered ring is 2.70 × 105 times faster than its acyclic counterpart (1a: phenyl ethyl chlorophosphate) because of great positive value of the entropy of activation of 1c (ΔS≠ = +26 eu) compared to negative value of 1a (ΔS≠ = –24 eu) over considerably unfavorable enthalpy of activation of 1c (ΔH≠ = 20.5kcal mol–1) compared to 1a (ΔH≠ = 12.7 kcal mol–1). Great enthalpy and positive entropy of activation are ascribed to sterically congested transition state (TS) and solvent structure breaking in the TS. A concerted mechanism involving a change of nucleophilic attacking direction from a frontside attack with the strongly basic pyridines to a backside attack with the weakly basic pyridines is proposed on the basis of greater selectivity parameters (ρX = –1.99 and βX = 0.41) with the strongly basic pyridines compared to those (ρX =–0.42 and βX = 0.07) with the weakly basic pyridines.
Kinetics and Mechanism of Pyridinolysis of O,O-Diethyl S-Aryl Phosphorothioates
하시라니바라이,이해황 대한화학회 2014 Bulletin of the Korean Chemical Society Vol.35 No.5
The kinetic studies on the reactions of O,O-diethyl Z-S-aryl phosphorothioates with X-pyridines have been carried out in dimethyl sulfoxide. The free energy correlations with X in the nucleophiles are biphasic concave upwards with a break point at X = H, while those for substituent Z variations in the leaving groups are linear. The negative sign of ρXZ implies that the reaction proceeds through a concerted mechanism for both the strongly and weakly basic pyridines. The biphasic concave upward free energy relationships with X are rationalized by a change in the nucleophilic attacking direction from frontside with the strongly basic pyridines to backside with the weakly basic pyridines.
Kinetics and Mechanism of the Anilinolysis of Bis(aryl) Chlorophosphates in Acetonitrile
하시라니바라이,이해황 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.6
The nucleophilic substitution reactions of bis(Y-aryl) chlorophosphates (1) with substituted anilines and deuterated anilines are investigated kinetically in acetonitrile at 35.0 ^oC. The kinetic results of 1 are compared with those of Y-aryl phenyl chlorophosphates (2). The substrate 1 has one more identical substituent Y compared to substrate 2. The cross-interaction between Y and Y, due to additional substituent Y, is significant enough to result in the change of the sign of cross-interaction constant (CIC) from negative ρ_(XY) = –1.31 (2) to positive ρ_(XY) = +1.91 (1), indicating the change of reaction mechanism from a concerted S_N2 (2) to a stepwise mechanism with a rate-limiting leaving group departure from the intermediate (1). The deuterium kinetic isotope effects (DKIEs) involving deuterated anilines (XC_6H_4ND_2) show secondary inverse, k_H/k_D = 0.61-0.87. The DKIEs invariably increase as substituent X changes from electron-donating to electron-withdrawing,while invariably decrease as substituent Y changes from electron-donating to electron-withdrawing. A stepwise mechanism with a rate-limiting bond breaking involving a predominant backside attack is proposed on the basis of positive sign of ρ_(XY) and secondary inverse DKIEs.
하시라니바라이,이해황 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.7
Kinetic studies for the reactions of O,O-dimethyl Z-S-aryl phosphorothioates with X-pyridines have been carried out in dimethyl sulfoxide at 85.0 ºC. The Hammett and Brönsted plots for substituent X variations in the nucleophiles are biphasic concave upwards with a break point at X = H, while those for substituent Z variations in the leaving groups are linear. The negative sign of the cross-interaction constant (ρXZ) implies that the reaction proceeds through a concerted mechanism for both the strongly and weakly basic pyridines. The magnitude of ρXZ (= –0.35) for the strongly basic pyridines is greater than that (ρXZ = –0.15) for the weakly basic pyridines, indicating a change of the nucleophilic attacking direction from frontside for the strongly basic pyridines to backside for the weakly basic pyridines. The early transition state is proposed on the basis of the absence of positive deviations from both the Hammett and Brönsted plots for the strong π-acceptor, X = 4-Ac,and small values of ρXZ and βX.